Copy control using digital speed bumps

ABSTRACT

A digital media recorder and a method of controlling such are provided. During attempts to copy media content, sub-sequences are extracted from an input media sequence. A digital fingerprint of the sub-sequence is calculated and compared with at least one first reference fingerprint from a database. The outcome of the comparison determines the action to take in the further processing. Recording of the input media sequence on a media carrier is either allowed or obstructed, e.g. disallowed. In the case recording of the sequence is allowed, the database is updated with information that the digital media sequence has been recorded.

TECHNICAL FIELD

The present invention relates in general to the field of copy protectionof digitally recorded media, and in particular to a method forcontrolling a digital media recorder and such a recorder.

BACKGROUND

More or less unauthorized copying of media content that is copyrightprotected has been an important issue for a long period of time. Forexample, audio records have been copied onto cassette tapes andtelevision programs and films have been copied onto video tape.Unauthorized copies of such types of analog recording media have allbeen marred by at least a slight decrease of quality as compared to theoriginal recordings.

However, the issue has become even more important as the media industryhas entered “the digital era”. Music and films are now being distributedin digitally encoded form and copies of these are usuallyindistinguishable from the original, creating an even bigger market for“pirate” of media content.

To illustrate the situation one can consider the recordable compactdisc, i.e. the CD-R. These are usually intended for recording audiocontent. However, any media content may be recorded on such discs.Moreover, while the following discussion will be exemplified by CD-R,there exist other digital recording media capable of recording media inthe form of, e.g., films that are equally relevant for the discussion.

Ever since its market introduction, CD-R has been an overwhelmingsuccess story. One of the main factors contributing to its rapidacceptance is that consumers now have the possibility to make digitalquality copies of the most popular audio format—the Compact Disc—thatwill play in any CD player. Whereas CE style CD recorders, i.e.dedicated digital audio copying devices, have to implement the SerialCopy Management System (SCMS), which limits duplication of copyrightasserted discs to first generation copies, there are no built-inlimitations for PC based CD recorders. The latter has become a hugeproblem from the perspective of the content owners, which are facing thehorror scenario that immediately after release of, e.g., a new musicalbum, large numbers of CD-R copies are traded or offered for sale onschool yards and similar environments. Consequently, and especially incombination with the mp3 phenomenon on the Internet, content ownersconsider CD-R a major factor in the stagnating growth of CD sales.

Technical measures that prevent misuse of recorders, such as makinglarge numbers of copies are therefore highly desirable. At the same timethe convenience of the devices should not be compromised, e.g. ifcopying is allowed by the owner of the content, then one should be ableto do so at high speed.

A prior art solution within the technical field of copy protection ofdigital data is presented in the International Patent Applicationpublished with the number WO 00/04688. There, a method and a system forprotecting digitally watermarked media content includes generatingdigital tickets associated with the media content. The ticket holdsinformation regarding a receiver and the copy protection status of thecontent as well as the digital watermark. The content of the ticket isprocessed by the receiver in order to determine whether or not thereceiver is allowed to copy the content.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a solution to a problemof how to provide a more flexible handling of copy protection of digitalmedia content.

According to a first aspect, the invention as claimed in claim 1 belowprovides a solution by way of a method of controlling a digital mediarecorder capable of recording digital media sequences on a digital mediacarrier. A sub-sequence is extracted from an input media sequence, suchas an audio or a video sequence. A digital fingerprint of thesub-sequence is calculated and compared with at least one firstreference fingerprint, which is fetched from a primary database offingerprints. The outcome of the comparison yields a first comparisonvalue to be used in determining the action to take in the furtherprocessing. Depending on the first comparison value, recording of theinput media sequence on the media carrier is either allowed orobstructed, e.g. disallowed. In the case recording of the sequence isallowed, the primary database is then updated with information that thedigital media sequence has been recorded on the media carrier.

Preferably, the primary database of fingerprints includes a copy countnumber and a copy limit number associated with fingerprints in the list.Then, the step of comparing the sub-sequence fingerprint with the firstreference fingerprint includes comparing the copy count number and thecopy limit number and the step of updating the primary database includesupdating the copy count number associated with the fingerprint.

In order to properly handle multiple occurrences of a sub-sequencewithin a media sequence, the invention preferably further involvescomparing the sub-sequence fingerprint with at least one secondreference fingerprint, said second reference fingerprint being fetchedfrom a secondary temporary database of fingerprints. This comparisonyields a second comparison value, which is used to determine the furtherprocessing. Depending on whether or not the second comparison valueindicates that the fingerprint exists in the secondary database, thefingerprint is stored in the secondary database. The primary database isfinally, when recording is completed, updated with information from thesecondary database.

The recorder checks if any recording that is being made, has been madepreviously by looking up the fingerprint in the primary database. Ifthat is the case, some appropriate action is taken, such as aborting therecording, or adding noise etc. Since the database has a finite size,older entries are removed in favour of newer ones, preferably on a firstin-first out basis, which means that after a while recordings that wereblocked will be permitted again. This results in that, within a presetamount of time, as determined by the size of the database, duplicaterecordings are prohibited, but independent of the speed a whichrecordings are made.

It is to be noted that the addition of a copy count and copy limit witheach data base entry allows duplicates to be made in series of more thanone recording. For example if the copy limit is set to 3, a series ofthree duplicates can be made. Subsequently the user has to make a largenumber of other copies, and next a new series of three copies can bemade etc.

For any new recording it is verified that the database does not containits fingerprint, or if it does, that the maximum number of copies hasnot yet been made. Otherwise, the recording shall be prohibited,continued with reduced quality, or some other appropriate action shallbe taken. That is, the recorder remembers what recordings have beenmade, by storing fingerprints in the primary database.

In other words, the technical effect of the present invention can bedefined by the concept of a “speed bump,” which does not prevent copiesof being made, but rather limits the rate at which those copies can bemade. In its basic form the concept is straightforward: let recordersprohibit more than a given number of copies to be made within a giventime frame.

In order for the proposed speed bump mechanism to be effective,especially in the PC world, it should not be thwarted easily by makingimperceptible changes to the digital content of the media. This rulesout implementations that rely solely on cryptographic hash functions.However, a viable alternative to use is the robust audio hashing, orfingerprinting-, technique disclosed in the following paper: JaapHaitsma, Ton Kalker and Job Oostveen, “Robust Audio Hashing for ContentIdentification,” Content-Based Multimedia Indexing conference 2001,Brescia, Italy. This technique allows extraction of robust features fromthe recorded media content, which a recorder can keep in an internaldatabase.

An advantage of the proposed mechanism is that no special preparation ofthe original media content is required as is the case with prior artsystems that rely on signaling by embedded watermarks. This is also truefor the recordings (e.g. remarking is not necessary). Thereforeaudibility issues do not play a role. Furthermore, intentional signaldistortion threats, e.g. in order to remove watermarks, are non-existenteither.

Another advantage of the invention is that usage for personal purposesis effected only to a small degree—depending on the permissible copyrate—while usage for (semi-) business purposes is substantiallyfrustrated.

Yet another advantage is that also in PC based recorders the speed bumpmechanism can operate autonomously, i.e. without help from the mainprocessor of the PC, when realized in a separate hardware module in therecorder itself as will be discussed in some detail below.

A further advantage of the speed bump mechanism according to theinvention is that the fingerprinting technology itself does not need tobe standardized-it may even yield a competitive advantage to keep itproprietary just the concept itself and the effectiveness of the speedbump, i.e. the maximum number of copies per series and the amount oftime that should pass until another series of copies is permitted.

According to a second aspect, the invention as claimed in claim 7 belowprovides a solution by way of a digital media recorder capable ofrecording digital media sequences on a digital media carrier, thetechnical effect and advantages of which correspond to the first aspectof the invention as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

A digital media recorder and a method of controlling such a recorderwill now be presented with reference to FIGS. 1, 2 and 3, where:

FIGS. 1 and 2 show schematically a digital media recorder according tothe present invention, and

FIG. 3 shows a flow chart of a method according to the presentinvention.

PREFERRED EMBODIMENTS

Although the embodiments will discuss only audio sequences and useterminology relating to audio recordings, other types of media areconsidered to be equivalents and will not be discussed separately.Moreover, it is to be understood that the invention is applicable toother kinds of digital recording media than the exemplified CD-R, suchas media that are based on magnetic recording techniques.

FIGS. 1 and 2 show, respectively, a digital recorder 100,200 comprisingan input/output unit 102,202 connecting to a digital media source101,201, memory 103,203, a processing unit 104,204 and a recording unit105,205 capable of receiving removable blank recording media 108,208such as CD-R.

As FIG. 2 illustrates, a separate control unit 209 may be present inaddition to the processing unit 204. As the skilled person realizes, allunits are connected via a bus 106,206 and, as illustrated in FIG. 2, mayalso include a connection 207 to a computer. Media content to be handledby the recorder 100,200 originates in a media source 101,201. As theskilled person realizes, such a media source 101,201 may be in the formof a data stream from an external computer, a digital output from adigital playback device etc.

As will be evident from the description to follow of a method accordingto the invention, the speed bump mechanism does not necessarily work onthe level of albums or tracks, but rather on the basis of recordingtime, i.e. sub-sequences of tracks or albums. The flow chart in FIG. 3shows a schematic overview of the algorithm. There are two databasesthat play a role: a primary database that contains fingerprints ofrecordings made on discs prior to the current one, and a secondarydatabase that contains those of the current disc. Both databases arerealized, as the skilled person understands, in the memory 103,203 ofthe recorder.

With reference to the flow chart in FIG. 3 as well as to thearrangements in FIGS. 1 and 2, a method according to the invention willnow be described. The method is preferably realized in the form ofcontrol sequences, i.e. software, stored in the memory 103,203 of therecorder 100,200. The software is run by the processor 104,204, the copycontrol unit 209 and/or by both processor 104,204 and control unit 209in cooperation.

Furthermore, the method assumes that a recording medium 108,208 in theform of a disc (e.g. CD-R) is inserted into a recorder according to theinvention, such as a recorder disclosed in FIGS. 1 and 2. Moreover,reference will be made to the primary and a secondary database.

Beginning the inventive method, in an input and extraction step 301fingerprints are extracted on a continuous basis from the audio contentthat is being received from the media source 101,201 and that isintended for recording.

Each of the extracted fingerprints is compared to a primary database fora match in a matching step 302. If no match is found, implying that arecording of the sequence is authorized, the method continues in astorage determination step 305. During the storage determination step305 it is decided whether or not the fingerprint is to be stored in thesecondary database. The decision is preferably based on criteriaregarding time intervals, i.e. the duration of the sub-sequence inquestion. Another criteria to select the fingerprint for storage may bebased on properties of the fingerprint itself. Any combination ofcriteria may also be used. These criteria will be discussed in some moredetail below

Continuing the inventive method, if a matching entry that has reachedthe copy limit is found in the matching step 302, a check is made in achecking step 303 whether the copy limit has been reached. Anappropriate action will be taken in an action step 304 if the copy limithas been reached. The action taken in step 304 preferably has the effectof degrading the recording, hence decreasing the “value” of therecording, and includes such actions as aborting the recording process,continuing the recording process at a reduced quality as well asnotifying a user of the action taken.

However, if the matching entry has not yet reached the copy limit, as ischecked in a copy limit checking step 303, the fingerprint is stored inthe secondary database, as indicated in a storage step 307. If thefingerprint is already present in the secondary database, there is noneed for storing it again, as is indicated by the checking step 306.

The step of recording then takes place in a recording step 308 andproceeds according to procedures known in the art.

In a checking step 309, it is decided whether or not the recording isfinished. If not, control returns to the step of input and extractionstep 301.

When all recordings have been made correctly and also when the currentdisc is ejected from the drive, as checked in checking steps 310 and311, the primary database is updated from the secondary database in anupdating step 312. This updating step 312 involves incrementing the copycounters of the fingerprints that occur in both databases, and movingthe remaining fingerprints from the secondary to the primary databaseusing a first-in first-out strategy.

The above algorithm correctly deals with repetitions within a piece ofaudio, which frequently occurs in, e.g., classical music. Basically theidea is that it is not important how many copies exist on a single disc,because these cannot be sold or given away separately. Therefore, theseare treated as a single instance.

The database is, as already presented, divided into two parts, namelythe previous history of fingerprints in the primary database, and thefingerprints of the current disc in the secondary database. To ensurethat the speed bump mechanism according to the invention is notactivated for failed recordings, only he primary database is used forverification purposes. Updating of this database does not occur untilthe disc has been ejected, and all recordings on that disc are correct.

As discussed above in connection with the storage determination step305, fingerprints of sub-sequences are stored in the secondary databaseat more or less regular time intervals. The effect of this is tointroduce a frequent degradation of a recording, decreasing the “value”of an unauthorized recording of the media sequence.

A more detailed discussion of the criteria regarding the regularity ofthe fingerprint storage will now follow. As already discussed, when acopy limit has been reached for a particular media sequence thefingerprint is to be stored in the secondary database. The regularity,i.e. time scale, of these storage actions is preferably dependent on thetype of content that is being copy controlled, and partly dependent onthe fingerprinting algorithm used. The time scale for the sub-sequenceshould be significantly shorter than a complete media sequence that isunder consideration. For example, for modern popular music where songstypically last no more than a few minutes, a one minute sub-sequence maybe appropriate. This means that if an unauthorized recording isattempted, there will be several instances of the action step 304 (e.g.distortions of the recorded signal with a preset or adaptive durationand intensity) in that recording, substantially decreasing the qualityof that (unauthorized) recording. For video sequences a sub-sequencetime interval of 5 or 10 minutes may be appropriate, since a movietypically lasts well over one hour. Alternatively, an additional randomtime interval may also be used.

The regularity of the storage of sub-sequence fingerprints may alsodepend on the fingerprinting algorithm that is used. For example, thealgorithm of the already referenced paper (Jaap Haitsma, Ton Kalker andJob Oostveen, “Robust Audio Hashing for Content Identification,”Content-Based Multimedia Indexing conference 2001, Brescia, Italy)generates a substantial amount of information in a short amount of time.Consequently such a method is preferably used in “burst mode,” i.e.fingerprint information is stored in the secondary database for shortcontent fragments only. Other fingerprinting algorithms are conceivablethat generate information at a much slower rate; it may even be possibleto store all information in the database, which would imply that theinterval decreases to zero and that the sub-sequence in fact is thecomplete media sequence.

An example of the performance of a method as described above will now bebriefly reported.

Based on the fingerprinting method disclosed in the previouslyreferenced paper: Jaap Haitsma, Ton Kalker and Job Oostveen, “RobustAudio Hashing for Content Identification, ” Content-Based MultimediaIndexing conference 2001, Brescia, Italy, the following estimates forthe performance of the speed bump algorithm as presented above, can bemade. Needless to say, this is only one example and is included here forillustration purposes only. Other optimizations and choices arepossible, as the skilled person will realize.

Fingerprint information is generated at a rate of about 1 kB per 3audio-seconds. For each audio-minute the fingerprint of a contiguous ⅜audio-sec fragment is stored in the database, which takes about 16 bytesemploying a reasonable optimization technique. Assuming that a speedbump of 16 real-time hours is required and recording occurs at singlespeed, the primary and secondary database sizes should be about 15 kBand 1 kB, respectively. For searching the database a bit-error rate inthe fingerprints of 1-in-8 yields sufficient robustness against commonsignal processing “attacks” (e.g. all-band filtering, equalization,subsequent D/A and A/D conversions, and mp3 compression at 128 kbps).Assuming a brute force search strategy, it takes on average 4 bytecomparisons per fingerprint to decide that a there is no match, whichtranslates to a required memory bandwidth to the database of about 320kB/audio-sec. Finally, the false positive rate can be estimated to beabout 2×10⁻¹² per audio-sec. Note that at higher recording speeds thefigures for the primary database size, memory bandwidth, and falsepositive rate have to be adjusted accordingly to maintain theeffectiveness of the speed bump.

Hence, to summarize: a digital media recorder and a method ofcontrolling such is shown. During attempts to copy media content such asaudio or a video sequences, sub-sequences are extracted from an inputmedia sequence. A digital fingerprint of the sub-sequence is calculatedand compared with at least one first reference fingerprint from adatabase. The outcome of the comparison determines the action to take inthe further processing. Recording of the input media sequence on themedia carrier is either allowed or obstructed, e.g. disallowed. In thecase recording of the sequence is allowed, the database is updated withinformation that the digital media sequence has been recorded. This hasthe effect of a “speed bump,” which limits the rate at which thosecopies of media content can be made, i.e. the effect is that ofprohibiting more than a given number of copies within a given timeframe.

1. A method of controlling a digital media recorder capable of recording digital media sequences on a digital media carrier, comprising the steps of: extracting, from an input media sequence, a media sub-sequence, calculating a sub-sequence digital fingerprint from the media sub-sequence, comparing the sub-sequence fingerprint with at least one first reference fingerprint, said first reference fingerprint being fetched from a primary database of fingerprints, yielding a first comparison value, depending on the first comparison value, allowing or obstructing recording of the input media sequence on the media carrier, comparing the sub-sequence fingerprint with at least one second reference fingerprint, said second reference fingerprint being fetched from a secondary database of fingerprints, yielding a second comparison value, depending on the second comparison value, storing the fingerprint in the secondary database, depending on at least the first comparison value, updating the primary database with information from the secondary database that the digital media sequence has been recorded on the media carrier.
 2. A method according to claim 1, where the primary database of fingerprints includes a copy count number and a copy limit number associated with fingerprints in the list, where the step of comparing the sub-sequence fingerprint with the first reference fingerprint includes comparing the copy count number and the copy limit number and where the step of updating the primary database includes updating the copy count number associated with the fingerprint.
 3. A method according to claim 1, further comprising the step of removing older entries from the primary database in favor of newer entries so as to limit the size of the primary database to a predetermined number.
 4. A method according to claim 1, where the updating of the primary database is dependent on whether or not the recording of the at least one media sub-sequence is completed.
 5. A method according to claim 1, where the obstruction of the recording includes at least one of the actions: aborting the recording, reducing the quality of the recording, notifying a user of the obstruction.
 6. A method according to claim 1, where the extraction of the sub-sequence includes extraction during a predetermined time interval, said time interval having a length determined at least partly by the type of the media sequence.
 7. A digital media recorder capable of recording digital media sequences on a digital media carrier, comprising: means for comparing the sub-sequence fingerprint with at least one second reference fingerprint, said second reference fingerprint being fetched from a secondary database of fingerprints, yielding a second comparison value, means for storing the fingerprint in the secondary database means for extracting, from an input media sequence, a media sub-sequence, means for calculating a sub-sequence digital fingerprint from the media sub-sequence, means for comparing the sub-sequence fingerprint with at least one first reference fingerprint, said first reference fingerprint being fetched from a primary database of fingerprints, yielding a first comparison value, means for analyzing the first comparison value, means for recording the input media sequence on the media carrier, means for obstructing recording of the input media sequence on the media carrier depending on the first comparison value, means for updating the primary database with information from the secondary database that the digital media sequence has been recorded on the media carrier.
 8. A recorder according to claim 7, where the primary database of fingerprints includes a copy count number and a copy limit number associated with fingerprints in the list, where the means for comparing the sub-sequence fingerprint with the first reference fingerprint includes means for comparing the copy count number and the copy limit number and where the means for updating the primary database includes means for updating the copy count number associated with the fingerprint.
 9. A recorder according to claim 7 being arranged to remove older entries from the primary database in favor of newer entries so as to limit the size of the primary database to a predetermined number.
 10. A recorder according to claim 7, where the means for updating the primary database are arranged to operate in dependence on means capable of establishing whether or not the recording of the at least one media sub-sequence is completed.
 11. A recorder according to claim 7, where the obstruction means includes obstructing means capable of at least one of the actions: aborting the recording, reducing the quality of the recording, notifying a user of the obstruction.
 12. A recorder according to claim 7, where the means for extraction of the sub-sequence includes means for extraction during a predetermined time interval, said time interval having a length determined at least partly by the type of the media sequence.
 13. A computer comprising a recorder according to claim 7 wherein the computer is configured to control the recorder.
 14. A method as in claim 1 wherein the secondary database updates the primary database in response to ejecting the media carrier.
 15. A recorder as in claim 7 wherein the secondary database updates the primary database in response to ejecting the media carrier.
 16. A computer as in claim 13 wherein computer is configured to update the primary database with the secondary database in response to ejecting the media carrier. 